Thanks to assistance from RME we now have Fireface devices and documentation to assist in the development of the FFADO RME driver. Some low-level changes have been flowing into the development trunk for a few weeks now and high-level functionality will follow once the necessary parts are in place. There is no ETA at this stage, but support for RME Fireface devices is on its way.
Update: 6 January 2011: progress has been slower than I wanted but steady, and I think the end is in sight. Check out the extended update posted on the FF400/FF800 device information pages. In short, it's hard to give specific ETAs because of "real life" commitments, but at this stage I'm hoping to get the FF400 driver into a state fit for wider testing around Feb/March, with similar FF800 support to follow around Q2 this year.